[zhangzhenghao]

Summary

• Replace the Windows ARM64 WinGet FFmpeg package with the user-requested tordona/ffmpeg-win-arm64 build, pinned to 9.0.2 essentials shared.
• Verify the archive SHA-256, extract with 7-Zip and export the directory containing ffmpeg.exe through GITHUB_PATH.
• Remove the ineffective -cpuflags 0 experiment: its CI still crashed during mono WAV-to-FLAC conversion with exit code 3221225477.
• Keep all other platforms, compiler settings and audio tests unchanged. This PR remains independent of ci: publish Python CPU wheels and sdist to PyPI #35.

Verification

• Downloaded the pinned archive and verified its published SHA-256 locally.
• Inspected the archive: ffmpeg.exe and runtime DLLs are together under its bin directory.
• actionlint v1.7.12 and git diff --check: passed.
• Windows ARM64 configure/build/CTest/install: passed on commit 864f882, including all 25 CTest tests.
• All five native CI platform jobs and all four Python jobs passed on that head.
• Verified native run: https://github.com/gorse-io/clap.cpp/actions/runs/40616285291